There are hydraulically driven vehicles known in the related art such as wheel hydraulic excavators, driven to travel by a driving motor that, in turn, is driven on pressure oil delivered from a hydraulic pump driven by a prime mover, the flow rate and the direction of which are controlled through a control valve (see, for instance, patent reference literature 1). In this type of vehicle, the control valve is switched by stepping on an accelerator pedal, and as the load pressure at the traveling motor increases, the motor speed is controlled by increasing the displacement of the traveling motor. In addition, a counterbalance valve is disposed at a conduit connecting the control valve to the traveling motor and by switching the counterbalance valve to the neutral position as the motor drive pressure becomes lowered, a braking pressure is generated at the conduit disposed on the output side of the traveling motor, thereby inhibiting the motor from overspeeding while the vehicle travels downhill or the like.    Patent reference literature 1: Japanese Laid Open Patent Publication No. H8-270788